Optical glass



Aug. 15, 1939 G.' W. MOREY OPTICAL GLASS Original Filed Aug. 19, I936Reias ue'd in. 15, 1939 U ITED ST TES enus;

PATENT. OFFICE 21,175 v or'rrcsr. cuss George W. Morey, Chevy Chase,

Md., assignor,

by mesne assignments, to Eastman Kodak ."Company, Jersey Gityr N. 1., acorporation New Jersey Original No. 2,150,694, dated March 14, 1939, Se-

rial No. 96,844, August 19, 1936. Application for reissue May 9, 1939,Se 'al No. 273,218. In Great Britain September 3, 1935 15 Claims. (61.106-361) primarily silicate glasses with a definitely limited range ofoptical pro rties. This is especially true of glasses having an index ofrefraction 0 greater than 1.65 and places a limit upon the opticalperformancewhlch may be secured by the lens designer. In these glasses,having a reiractive index greater than 1.65 the dispersion is a definitefunction or the index and it is'difllcult, ii. not impossible, to attainwith these glasses the degree of correction required for certainexacting lens systems.

It is an object of this invention to provide new glasses having highrefractive indices and l possessing relations between refractivity anddispersion different from those of previously known glasses; and whichare of great chemical stability, notably fluid when molten so that theyreadlly rid themselves of all bubbles, hard enough to withstandmechanical abrasion and scratching, capable of taking a high polish,resistant toweather and conditions of use for a prolonged period, andcomposed of ingredients which are essentially non-volatile and stable attemperatures 'necessary in making glass.

Further objects and advantages 01' this invention will appear from thefollowing description when read in connection with the accompanyingdrawing, the single figure of; which is a diagram showing'the pointsobtained by plotting the dispersive ratios 1 of a number of glassesagainst their refractive indices for the D line (12D).

In this figure, the points corresponding to the new glasses heredisclosed are designated by capital letters, corresponding to theformulae here,- inaiter given. formula v and a is m be noted'that thevalue r the dispersive ratlo,..r,.is inmost instances greater than this.These optical properties are'oL-utility in the designing of objectives,and optical systems and apparatus.

means an inorganic amorphous mass; and the although its composition Thecurve :2 represents the It is further to be noted that, in everyinstance, the values of v and 11D are greater than the lines 11 and z.The line 1! is drawn through the IJOLI'HFS (7:65, 11D=1.60) and (#:25,7ZD=1.85) and is defined by the'equation 5 +2'oonn=3a5 The line 2 isdrawn through the second of the above definedpoints and point (11:15,nD=2.l0) and is defined by the equation- These newly discovered glassesare inorganic,

within a useful range and formed by fusion of certain oxides hereinafter more definitely specified.

When used in the claims the word glass word transparent means capable oftransmitting useful light without difiusion except that due torefraction. Claims specifying a glass batch are intended to include theelements originally added, whatever may be their proportion or con-,dition in the resultant glass.

From earliest times silica has been one of the chief ingredients ofglass and optical glass at present contains a substantial percentage ofsilica. The principal exceptions to this statement are certain glassesformerly manufactured, high in boric. oxide and/or phosphoric oxide,whose manufacture has been discontinued because of their low chemicalstability. These glasses, the

compositions of which were entirely different from those hereindisclosed, did not have very high indices and were not particularlyuseful to the lens designer. It is generallyaccepted that glass is a.mixture rather than a compound, and, 40

well known, prac-' tically nothing is known about its constitution.

In attempting to obtain a, glass of unique optical properties andespecially a glass. having a refractlve index: greater than 1.65 andxaunique dispersion, i. e., one which does not follow the flint glasstrend, it seemed reasonable to expect that its composition should bebuilt around the acid forming elements having relatively high atomicweights rather than silicon whose atomic to weight is less than 30. Ihave found by long experiment that such a glass may indeed be made usingthe oxides of certain elements, particularly certain of those in theeven series, and especially the eighth, in Groups III, IV, V and VI ofthe periodic table having atomic weights greater than practical use forvarious reasons, particularly their undes rable color absorption, theirpresent rarity or difficulty in obtaining them in commercial quantitiesor in purified form. However, I do not intend to exclude from. ,myinvention glasses whose color absorptions do not detract from theirusefulness in certain optical systems. All of the elements in the seriesmentioned which I have tried have, in certain combinations, formedglasses. Certain of these elements have more than one oxide and in suchcases is meant only that oxide having the formula characteristic of thegroup, namely X for the third group, X0 for the fourth group, X 0 forthe fifth group and X0 for the sixth group. Those elements, the oxidesof which when fused yield opaque or 'undesirably colored components areprincipally those having more than one oxide and it is possible that thecolor or opacity is due to the breaking down of the oxides and that ifthe pure oxide In general the materials comprising the formula arecarefully weighed, screened, well mixed and melted at a temperaturesufficient to melt all the ingredients, usually about 2000 to 2500 l".

When they are thoroughly melted and mixed, the batch is poured into acontainer heated to the region of 1000 F. and placed in an annealingoven at a temperature of from 1300 to 1500 1". and slowly cooled,although all of these temperatures are variable with the composition ofthe glass. Because of the high fluidity, the batch may be well mixed bystirring or by pouring back and forth between two crucibles.

The elements which I have found especially useful are those in theeighth series and especially lanthanum and tantalum, and these tw incombination with other oxides, such as tit: nium, thorium, zirconium andtungsten, seem be especially useful. The chemical composition of theglass resulting from the formulae hereinafter given cannot now be statedwith certainty, but the advantages of using thelingredientsgiven and theimproved properties of glass are very pronounced, whatever may be theactual constitution of the glass. It is very possible that the noted'disadvantages of certain of the oxides may be partially or completelyovercome.

' It has been found that tantalum oxide alone makes a very satisfactoryglass, but it is to be sults arethe followingparhbeinggivenby weight.nisiobeunderszoodthanneacncase the oxide is used unless otherwisespecifically stated:

Example A.-Equal parts by weight of titanium and tantalum oxides iEXarnplcs B O D E F Lanthauum 42 51 60 50 Sodium s l Examples G H'litaniuzm. 2o Zirconium TantalunL. 3U 50 Silicon 50 n Examples... I J KM P Q R Lanthanum 26.3 27.2 49.2 37.5 36 %.7 22.2 Tantalum r. 28.3 27.225 29.2 28 26.7 22.2 Thorium 20.2 18.5 9.8 16.7 16 26.7 fl.2 Zirconium4.9 Boron 22.7 22.6 9.8 16.6 20 19.9 33.4 Borax 4.5 4.5 3.3

Example L Lanthanum -00 Zirconium 8. 5

The batches, whose compositions are given above, produce excellentoptical g having extremely high indices of refraction and much lowerdispersions than do glasses of the flint series: Examples fend K beingnotably clear. These glasses are shown in the accompanyingdrawing fromwhich'their unique optical characteristics are readilyapparent. Thenumerical values of the refractive indices of some of these glasses andtheir dispersive indices used in determiningtheirpositionin thedrawingarelisted below, the dispersive index (r) having the valuev 'nD1nF-nC 'nG v Examples I wish to point out, however, that, while Iconsider all the formulae given above to be included within the scope ofmy invention as broadly stated in this specification and covered in theclaims appended hereto, certain of the formulae given are, so far as thespecific combinations and proportions are concerned, the work of Leon W.

Eberlin, in Whose name applications covering lum oxide need not becompletely free of columbium, and the small amount of hafnium, which isusually present in small quantities in all commercial zirconium, doesnot appear to have any harmful effect.

In general and particularly in formulae B to G inclusive, the lanthanumoxide may be replaced in whole or in part by yttrium oxide and thezirconium oxide may be replaced with thorium oxide, and the lattersubstitution is especially suggested in formula C.

As instances in some of the formulae, it may be desirable or necessaryto adda glassifier or fluxing agent such asboric oxide or borax, orother borates- It will be also understood that the batch compositions,given above, are not 'at all rigid and that various ingredients, such assmall amounts of. lithium or sodium oxide, may be used without departingfrom the invention. In some cases, it may be desirable to include theoxide of either rubidium or cesium, since these glasses may be referredto roughly as being acid types of glass.

Although a number of the rare earths which are very expensive anddiflicult to obtain have not been tested for their glass formingproperties, all of the more readily obtainable elements of the evenseries in Groups III, IV, V and VI, of the periodic table having atomicweights greater than 47 have been tried and they have been found to bewell suited to the making of high quality glass. Although it is truethat certain of them, such as vanadium, uranium and cerium, impart somecolor in the glass, this color is not necessarily disadvantageous forall uses.

- Although the preferred examples of these new glasses contain nosilicate I consider as within the scope of my invention all glasseswhich, even though they may contain silicates and other compounds,contain a considerable proportion of the oxides above pointed out andhave the characteristic properties attributable to these oxides,

and two examples are given, which include aconsiderable proportion ofsilica. In general, however, I do not propose to use silica to an extentapproaching 25% of the total, andprefer it to be less than 10%.

As is evident from the formulae and specification the oxides which Ihave found most useful. are those of titanium, zirconium, lanthanum,tantalum, thorium and tungsten and to a less extent yttrium, columbiumand halfnium, and the glasses having a high proportion of these haverefractive and dispersive values greater than the curve a: on the chart.The properties of these glasses now seem to be of the greatest value foroptical instruments. However, a small proportion of these materials, asin Examples N and 0, give glasses having new properties attributable tothe presence of these materials, and all glasses, particularlynonsiiicate glasses, having these oxides in suflicient amounts andproportions to yield glasses having these distinguishing properties Iconsider as within the scope of my invention.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent isz 1. A transparent optical glass having anindex of refraction (nD) for the D-line greater than 1.65 and adispersive index greater than both 385--200 nD and 99--40 nD, resultingfrom fusion of a glass batch containing less than 10% silica andcontaining at least 20% by weight of oxides selected from the groupconsisting of the following elements: titanium, yttrium, zirconium,columbium, lanthanum, hafnium, tantalum, tungsten and thorium.

2. A non-silicate transparent optical glass having an index ofrefraction (nD) for the D-line greater than 1.65 and a dispersive indexgreater than both 385200 nD and 9940 11D resulting from fusion of aglass batch containing at least twenty percent by weight of oxidesselected from the group consisting of the following elements: titanium,yttrium, zirconium, columbium, lanthanum, hafnium, tantalum, tungstenand thorium.

3. A non-silicate transparent optical glass having both an index ofrefraction (nD) for the D line and a dispersive index (I greater thanboth v=385200 11D and v=99-40 nD resulting from fusion of a glass batchcontaining at least twenty percent by weight of oxides selected from thegroup consisting of the following elements: titanium, yttrium,zirconium, columbium, lanthanum, hafnium, tantalum, tungsten andthorium.

4. A non-silicate transparent optical glass having both an index ofrefraction (11D) forthe D- line and a dispersive index greater thanv=38381/nDl.75 resulting from fusion of a glass batch containing atleast twenty percent by weight of oxides selected from the .groupconsisting of the followingelements: titanium, yttrium, zirconium,columbium, lanthanum, hafnium, tantalum, tungsten and thorium. I

5. A glass resulting from fusion of a glass batch containing the oxidesof tantalum and lanthanum to a total of at least 40%, and having anindex of refraction greater-than 1.70. I

6. A nonsilicate glass resulting from fusion of a glass batch containingthe oxides of tantalum and lanthanum to a total of at least 40% of thetotal by weight.

7. A glass resulting from fusion of a glass batch containing the oxidesof lanthanum, tantalum and thorium to an amount equal to at least 65% ofthe totalby weight;

8. A glass resulting from fusion of a glass batch containing the oxidesof lanthanum, tantalum and thorium to an amount equal to at least 65% ofthe total by weight and also containing boric oxides.

9. A glass resulting from fusion of a batch containing at least twentyper cent of weight of lanthanum oxide.

10. A glass resulting from fusion of a batch containing at least twentypercent by weight of tantalum oxide.

11. A glass batch containing at least fifty percent by weight of oxidesselected from the group consisting of the following elements: titanium,zirconium, lanthanum, tantalum, tungsten and thorium.

12. A glass batch containing at least twenty percent by weight of oxidesselected from the' group consisting of the following elements: titanium,zirconium, lanthanum, tantalum, tungsten and thorium and containing notover twenty five percent of silica.

13. A glass batch containing at least forty percent by weight of theoxides "of zirconium and lanthanum.

14. A method of manufacture of optical glasses having a refractive indexgreater than 1.65 which comprises fusing with suitable fluxes an oxideor oxides selected from the group consisting of the following elements:titanium, zirconium, lanthanum, tantalum, thorium, tungsten, yttrium,columbium and hafnium, the latter being present to a total amount equaltoat least fifty percent by weight of the batch.

15. A method of manufacture of optical glasses having a refractive indexgreater than 1.65 which comprises fusing with suitable fluxes, and inthe absence of silica, an oxide or oxides selected from the groupconsisting of the following elements: titanium,- zirconium, lanthanum,tantalum, thorium, tungsten, yttrium, columbium and hafnium, the latterbeing present to a total amount equal to at least fifty percent byweight of the batch.

GEORGE W. MOREY.

